Thanks for your effort so far.
I just updated the original page. Everything works up to this point (doesnt matter if I use 128MB or 256 MB memory limits). The trouble starts when I update the theme – and in my case I do this by copying and extracting the new theme-zip-file over the old one.
The site is runnin on 1.3 so far. The newest zip holds 1.5.0.
Maybe this last step is wrong. How is your intended way to update xsports?